ATV transmission

ABSTRACT

An all terrain vehicle comprises a frame supported by at least a left wheel and a right wheel. The left wheel and the right wheel being connected to said frame by a left suspension and a right suspension respectively. The independently suspended wheels preferably are drive wheels. The wheels are driven by an engine through a transmission. The transmission is connected to the left wheel by a left half shaft and to the right wheel by a right half shaft. Constant velocity couplings are used to coupling the half shafts to the respective wheels and to the transmission. The constant velocity couplings connecting the two half shafts to the transmission are joined in a single housing. The housing includes a body portion and a gear portion. The two portions can be integrally formed. A left cage and a right cage are mounted within a left axial bore and a right axial bore formed in the body portion. The cages are secured for rotation with the body portion but can move axially within the respective bores. The two half shafts similarly are secured for rotation with the cages. The half shafts can be connected to the cages with respective inner members. The two bores can be combined or separated by a dividing wall.

This is a continuation of application Ser. No. 09/505,543 filed Feb. 17, 2000, now U.S. Pat. No. 6,250,415.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to drive arrangements for all terrain vehicles. More specifically, the present invention relates to separated engines and final drive assemblies for use in all terrain vehicles.

2. Related Art

All terrain vehicles are constructed for use in all kinds of rough, rocky and uneven terrain. The vehicles generally comprise a frame that defines an engine compartment, an engine positioned within the engine compartments and a transmission that drives a set of wheels with power from the engine. The transmission typically is included within a transmission case that is directly connected to the engine and generally powers the rear wheels through a shaft and differential assembly. Preferably, substantial clearance is maintained between the vehicle and its associated components and the ground over which the vehicle is being operated.

In some off road vehicles, the drive wheels are independently suspended.

Independently suspended wheels allow the wheels to make contact with the ground independently of the positioning of the associated wheel. For instance, the motion of a right rear wheel is not necessarily tied to the motion of a left rear wheel. The independent suspended wheels, however, have wheel travel limitations. Wheel travel is particularly important in off road vehicles, especially with respect to independently suspended drive wheels.

In vehicles employing independently suspended drive wheels, the drive wheels are separately powered through independent half shafts. The half shafts preferably are coupled to the transmission and to the respective wheels by constant-velocity couplings. While the vehicle is running, the suspensions absorb shocks and impacts from the ground. Thus, the wheels move in a vertical direction relative to a frame of the vehicle. As the wheels bounce up and down, the drive shafts pivot with respect to the transmission. The pivoting causes a change in a crossing angle defined by a center of the constant-velocity coupling and the center of the drive shaft.

SUMMARY OF THE INVENTION

By increasing the available travel of the wheels independent of the other, operation of the vehicle is improved. For instance, the suspension system is better able to absorb the impact caused by sudden jolts or large bumps. In addition, the suspended wheel is better able to remain in contact with the ground. To increase the wheel travel, either the crossing angle or the length of the half shaft should be increased.

It has been discovered that increasing the crossing angle yields some undesirable results. For instance, by increasing the crossing angle, the joint is subjected to extreme wear. In addition, the joint is more likely to be damaged as the joint is reconfigured to expand the limits of the crossing angle.

Accordingly, the present invention increases the length of the half shafts; however, rather than simply increasing a lateral dimension of the vehicle to accommodate a pair of longer half shafts, the constant-velocity couplings have been reconfigured to reduce a lateral dimension of the pair of couplings. A variety of advantages stem from the changes, as will become apparent from the following detailed description.

Desirably, the improved transmission features a pair of constant-velocity couplings that have been integrated into a single housing. The housing desirably reduces the lateral dimension associated with the pair of couplings. In addition, the housing allows a reduced distance between the moving components that are positioned within the housing. The reduced distance and the reduced lateral dimension allows the length of each half shaft to be increased. Thus, while the crossing angle is minimized, the increased half shaft length results in increased wheel travel. The reduced crossing angle better protects the coupling. Moreover, the increased wheel travel improves vehicle performance. Furthermore, even through the half shaft length is increased, the overall width of the vehicle can remain the same or be decreased.

Accordingly, one aspect of the present invention involves an all terrain vehicle comprising a frame. A right wheel and a left wheel are independently mounted to the frame. An engine compartment is defined within the frame and an engine is mounted within the engine compartment. The engine drives the right wheel and the left wheel through a transmission. A right drive shaft connects the right wheel to the transmission and a left drive shaft connects the left wheel to the transmission. The right drive shaft and the left drive shaft are linked to the transmission through an output arrangement. The output arrangement includes a gear portion and a housing portion. The housing portion includes a left bore and a right bore. A left cage is positioned within the left bore and a right cage is positioned within the right bore. A left inner member is positioned within the left cage and a right inner member is positioned within the right cage. A proximal end of the left drive shaft is secured for rotation with the left inner member and a proximal end of the right drive shaft is secured for rotation with the right inner member. The left cage is secured for rotation with the housing portion and the right cage is secured for rotation with the housing portion. The left inner member is secured for rotation with the left cage and the right inner member is secured for rotation with the right cage.

Another aspect of the present invention involves a constant velocity coupling comprising a housing. The housing comprises a cylindrical body, a ring gear extending about an exterior surface of the cylindrical body, a first axial bore extending into the cylindrical body and a second axial bore extending into the cylindrical body. The first axial bore and the second axial bore both have centerlines that are aligned with a centerline of the cylindrical body. A first cage is positioned within the first bore and is coupled for rotation with the cylindrical body. A second cage is positioned within the second bore and is coupled for rotation with the cylindrical body. A first half shaft is coupled to the first cage for rotation with the first cage and a second half shaft is coupled to the second cage for rotation with the second case.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the present invention will now be described with reference to the drawings of a preferred embodiment, which embodiment is intended to illustrate and not to limit the invention, and in which figures:

FIG. 1 is a side view of a vehicle being constructed in accordance with certain features, aspects and advantages of the present invention, with certain internal components of the vehicle being shown in dashed lines and certain body components being shown in phantom lines;

FIG. 2 is a top view of the vehicle of FIG. 1 illustrating a placement of an engine and a final drive assembly;

FIG. 3 is a rear view of the vehicle of FIG. 1 illustrating a suspension arrangement and the placement of the final drive assembly;

FIG. 4 is a partial side view of the vehicle of FIG. 1 illustrating two positions of the final drive assembly relative to a frame assembly;

FIG. 5 is a further partial size view of the vehicle of FIG. 1 illustrating certain shafts of the final drive assembly in cross section and a transmission lock arrangement;

FIG. 6 is a cross section through FIG. 5 taken along the line 6—6 and illustrating a drive shaft drive arrangement; and

FIG. 7 is a cross section through FIG. 5 taken along the line 7—7 and illustrating a tension adjustment arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

With reference now to FIGS. 1 through 3, an all terrain vehicle is illustrated and is generally identified by the reference numeral 20. The vehicle 20 incorporates a transmission that is arranged and configured in accordance with certain features, aspects and advantages of the present invention. The illustrated vehicle 20 preferably is adapted for off-road operation; however, certain features, aspects and advantages that will become apparent below can be used in street vehicles. In addition, as the illustrated vehicle 20 is only a typical application for the present invention, other applications will become readily apparent to those of ordinary skill in the art. For this reason, many details of the illustrated vehicle 20 that do not require an understanding for one of ordinary skill in the art to practice the present invention will be omitted; however, the omitted details should be considered well-known to those of ordinary skill in the art.

With continued reference to FIG. 1, the vehicle generally comprises a frame assembly 22 that is supported by a set of wheels. In the illustrated arrangement, a spaced pair of front wheels 24 and a spaced pair of rear wheels 26 support the frame assembly 22. Of course, one or more than two front wheels and one or more than two rear wheels also can be used. The wheels 24, 26 preferably are a low-pressure, balloon-type of tire that is specifically designed for off-road use.

The frame assembly 22 generally is of a welded-up type comprising a number of tubular members connected by welds and fasteners. With reference to FIG. 1, the illustrated frame assembly 22 comprises an upper frame 28 and a lower frame 30. Both the upper frame 28 and the lower frame 30 preferably comprise a pair of members that are substantially mirror images of one another. As illustrated, the lower frame 30, preferably extends in a generally longitudinal direction from a forward bumper 32 to a seat rail 34 and has a portion that defines a plane that is substantially parallel to the ground G over which the vehicle is operated. The illustrated lower frame 30 bends downward and rearward from the forward bumper 32 and a rear portion 35 of the lower frame 30 bends upward and then forward to the seat rail 34. Such a construction generally defines an engine compartment 37 in which an engine 36 can be secured. The engine generally is secured between the front wheels and the rear wheels.

The illustrated upper frame 28 preferably extends in the same generally longitudinal direction from a forward portion of the lower frame 30 to a rearward portion of the lower frame. More specifically, the upper frame 28 extends upward from the lower frame 30 from a location slightly forward of an axis of rotation of the front wheels 24 and then bends rearward. The upper frame 28 also has a portion that extends substantially rearward before bending downward toward the lower frame 30. The illustrated upper frame 28 bends downward at a location just forward of a fuel tank 38 and connects to the lower frame 30 at a location just forward of the rear wheels 26.

A pair of bumper support bars 40 extend generally rearward from the bumper 32 and support the bumper 32 during frontal impacts. As illustrated, the support bars 40 desirably bend inward near the upper frame 28. In some arrangements, the support bars 40 extend beyond the upper frame 28 and the upper frame 28 is split with an upper portion being attached to the support bars 40 and a lower portion extending between the support bars 40 and the lower frame 30. In the illustrated arrangement, the support bars 40 are split into a forward portion and a rearward portion. The forward portion extends between the bumper 32 and the upper frame 28 while the rearward portion extends between the upper frame 28 and a supporting down tube 42.

The illustrated forward down tube 42 extends between the upper frame 28 and the lower frame 30 at a downwardly and rearwardly sloping angle. In the illustrated arrangement, the angle is rather steep and provides support while maintaining a construction that eases servicing of the internal components. Of course, a longer down tube 42 that extends at a less steep angle also can be used depending upon the application.

Any number of cross members 44 can be used to join the two sides of the frame assembly 22. With reference to FIG. 2, at least one cross member 44 is positioned between the forward most ends of the upper frame 28 or near the forward most ends of the upper frame 28 in the illustrated arrangement. Of course, any number of other cross members can be strategically positioned elsewhere within the frame assembly 22.

With continued reference to FIGS. 1 through 3, the seat rails 34 generally extend rearward from the upper frame 28. In the illustrated arrangement, the seat rail 34 has an elongated U-shape such that the two generally parallel legs of the seat rail 34 are formed of a single member. Of course, other constructions can also be used. The seat rail 34 generally is supported by the upper frame 28, the lower frame 30 and a rearward down tube 46. The illustrated down tube 46 extends in a steeply inclined forward angle but can incline less steeply in some arrangements.

The frame assembly 22 carries a number of body components. For instance, a front fender assembly 48 is secured to the frame assembly 22 and covers the front wheels 24 in a known manner. Similarly, a rear fender assembly 50 is secured to the frame assembly 22 and covers the rear wheels 26 in a known manner. A seat 52 and the fuel tank 38 also are secured to the frame assembly in a location generally defined between the front fender assembly 48 and the rear fender assembly 50. The fuel tank 38 preferably is positioned forward of the seat 52. More particularly, the fuel tank 38 is positioned below an upwardly sloping forward portion 54 of the seat 52 that lies generally forward of a rider position 56.

As is known, typically a rider sits upon the seat 52 with a leg positioned to either side of the seat 52 and with each foot resting on an associated foot rest 58. The foot rests 58 preferably extend between the front fender assembly 48 and the rear fender assembly 50 and preferably are positioned inboard of the outer surfaces of the rear wheels 26.

A fuel tank and engine compartment cover 60 extends rearward from the illustrated front fender assembly 48 and blends with the seat 52 at a rear end of the cover 60. In the illustrated arrangement, the cover 60 extends between two separate front fenders of the front fender assembly 48; however, the cover 60 and the front fender assembly 48 can be combined in some applications.

A steering handle assembly 62 extends down through the cover 60 from a location defined generally forward of the seat 52. The steering handle assembly 62 includes a number of controls that are well known to those of ordinary skill in the art. In addition, the steering handle assembly 62 generally is constructed to direct the vehicle 20 along a chosen operational direction by rotating the front wheels about a generally vertical axis or a pair of generally vertical axes. As such steering handle assemblies are very well known to those of ordinary skill in the art, and because the present steering handle assembly 62 does not form an integral part of the present invention, further description is deemed unnecessary.

With reference now to FIG. 3, the illustrated vehicle 20 also comprises an independent rear suspension system 63. While other types of suspension systems can be used in some arrangements, the illustrated independent rear suspension system is presently preferred. The illustrated suspension system 63, as will become apparent, is of the double-wishbone type; however, other types of independent suspension arrangements also can be used.

With continued reference to FIG. 3, a pair of pivotal connections 64 are provided on each side of the frame assembly 22. The illustrated pivotal connections 64 generally comprise a pin and sleeve arrangement is used; however, the pivotal connections 64 can be formed in any other suitable manner.

A pair of wishbones are connected to the frame assembly 22 through the pivotal connections 64. More specifically, an upper wishbone 66 and a lower wishbone 68 are connected to the frame assembly 22 with the pivotal connections 64. The wishbones 66, 68 are capable of pivotal movement relative to the frame assembly 22 about a first axis A and a second axis B, respectively.

The other ends of the wishbones 66, 68 are connected to a carrier hub 70. More particularly, the central regions of the wishbones 66, 68, which are positioned between the two pivotal connections 64 to the frame assembly 22 on each of the wishbones, 66, 68, are connected to by upper and lower pivotal connections 72. The generally parallel construction of the wishbones 66, 68 and the arrangement of the connections 64, 72 allow each of the rear wheels 26 to translate up and down without any significant variation in contact surface between the wheels 26 and the ground G.

The carrier hub 70 rotates about a third axis, C. The wheels 26 also rotate about the same third axis C. With continued reference to FIG. 3, the carrier hub 70 journals a stub shaft 74 on which a rim 76 is mounted using a hub arrangement (not shown). The wheels 26, of course, are mounted to the rims 76 in any suitable manner.

Movement of the wheels 26 relative to the frame assembly 22 preferably is damped and somewhat controlled using shock absorbers 78. The shock absorbers 78 can be of any suitable type and can be attached to the frame assembly and the suspension system through any suitable connection.

With reference again to FIG. 1, the illustrated wheels 26 are driven by a drive unit 77 that preferably includes the engine 36 and a final drive 81. While the illustrated vehicle 20 uses a two-wheel drive arrangement, the vehicle 20 also could use a four wheel drive arrangement in some applications. Moreover, one or more than two wheels can be driven in further arrangements, as is generally known to those of ordinary skill in the art.

The illustrated engine 36 generally has an engine body 79 that comprises a single cylinder and operates on a four-cycle principle. Of course, other numbers of cylinders and other operating principles (i.e., two-cycle, rotary) can be used in other arrangement. The illustrated engine is constructed in a well known manner and generally comprises a cylinder head 80, a cylinder body 82, and a crankcase 84. The head 80 and the crankcase 84 are positioned to opposite sides of the cylinder body 82. A piston (not shown) is preferably reciprocally mounted within the cylinder body 82 and the piston preferably drives an output shaft 86 through a suitable transmission 87 that is mounted within a transmission case 88 formed rearward of the crankcase 84.

Air is supplied to the engine for combustion through a suitable induction system. The illustrated system comprises an air filter 90 that is disposed beneath the cover 60 and that is positioned within a void 92 formed beneath the cover 60. This arrangement substantially protects the inlet to the induction system through the air filter 90 from large particles and water.

Air is delivered through the filter 90 to a charge forming device 94. In the illustrated arrangement, the air is delivered to a carburetor 94 for mixing with fuel; however, it is anticipated that the present invention also can be used with a fuel injected engine (i.e., direct injection, indirect injection). From the carburetor 94, the air-fuel mixture is supplied through an intake pipe 96 to a combustion chamber defined within the cylinder. The intake pipe 96 may be flow controlled using any suitable valve arrangement, which are well known to those of ordinary skill in the art.

After combustion, the exhaust gases are vented to the atmosphere through an exhaust system 98. The exhaust gases flow out of the combustion chamber into a first exhaust pipe 100. This exhaust pipe 100 turns the exhaust gas flow rearward and toward a muffler arrangement 102. The muffler arrangement 102 allows the gases to expand and controls the noise of the engine somewhat. The muffler arrangement 102 is preferably tucked under a portion of the frame assembly 22 for protection.

With reference now to FIG. 1, output from the output shaft 86 is transferred to the final drive 81 through a suitable transmission element. While some arrangements can employ a final drive that is integrally formed with the engine, in the illustrated arrangement, the final drive 81 is formed separate from the engine 36 and its associated transmission 88. The separation allows the two components to be positioned within the frame individually rather than having to build the engine and transmission and then position the assembly into the frame. Thus, the separation eases manufacture and assembly. In addition, by moving the final drive 81 toward the rear of the vehicle, the engine and transmission 88 can be more compactly constructed and the associated vehicle will benefit from a better weight distribution. Thus, the final drive preferably is positioned such that it would be intersected by drive shafts extending to the rear wheels. Of course, it could be moved forward or rearward of this position in some arrangements, but such a construction would unnecessarily complicate the construction of the vehicle 20.

A drive sprocket 110 is mounted on the output shaft 86 of the engine 36 and the transmission 88. A driven sprocket 112 is secured to an input shaft 114 of the final drive assembly 81. The driven sprocket 112 is driven by the drive sprocket 110 using a flexible transmitter 116. Together, the sprockets 110, 112 and the flexible transmitter 116 form a coupling transmission assembly 118. The coupling transmission assembly 118 is designed to transfer power between the transmission 88 and the final drive 81. Of course, in some arrangements, the driven sprocket 112 can be mounted to directly drive the rear wheels without the power passing through a final drive assembly 81. The sprockets 110, 112 can be pulleys, variable speed pulleys, or other types of flexible transmitter drive components. In addition, the flexible transmitter 116 can be a belt, chain, band or other continuously formed loop.

With reference now to FIGS. 5-7, the final drive 81 and its connection to the rear wheels 26 will be described in detail. The final drive 81 preferably comprises a reduction drive assembly that allows the output of the engine 36 to be converted into a desired operating speed for the vehicle 20. Thus, the final drive 81 comprises an upper casing 120 and a lower casing 122. The casings 120, 122 generally define a final drive transmission chamber 124. A number of shafts and gears are mounted within the chamber 124.

The input shaft 114 rotates about a fourth axis D, as does the driven sprocket 112. The input shaft 114 selectively drives an intermediate shaft 126 or a reverse shaft 128. More particularly, the vehicle 20 preferably includes a shifting arrangement that enables an operator to select either a forward mode of operation or a reverse mode of operation. The input shaft 114 thereby is selectively coupled to an intermediate shaft 126 or a reverse shaft 128 to accomplish such a mode of operation. The intermediate shaft 126 and the reverse shaft 128, in turn, are engaged with an output arrangement that will be described below.

With reference now to FIGS. 5 and 6, the shifting arrangement and the shaft arrangement will be further described. The final drive is shifted with a shift lever or push button that preferably is disposed proximate an operator of the vehicle 20. The shift lever or push button acts on a cable 130, which is preferably of the Bowden wire type. The cable 130, in turn, is connected to a pivot arm 132.

Movement of the cable effects a rotation of a shaft 134 to which the pivot arm 132 is secured. The shaft 134 preferably includes a pair of channels that extend around at least partially around the circumference of the shaft 134.

The first channel 136 has a changing profile. A sensor and ball arrangement 138 can detect the position of the shaft 134 from a position of the ball relative to the sensor. As the ball moves radially away from a center of the shaft, the sensor detects the movement and registers change in shift position. Similarly, as the ball moves radially toward a center of the shaft, the sensor detects the movement and registers the change in shift position.

The second channel 140 is in registry with a dog clutch 142 that translates along a shaft 146. As the dog clutch moves in the direction R, the dog clutch 142 urges a transfer gear 148 into engagement with a reverse gear 150. Similarly, as the dog clutch moves in the direction F, the dog clutch 142 urges the transfer gear 148 into engagement with a forward gear 152. If the dog clutch 142 is positioned between the two positions, neither gear 150, 152 is engaged and the final drive 81 is in a neutral position.

The driven sprocket 112 is secured to the input shaft 114. The input shaft is journaled by bearings 160 and sealed at both ends of the case 120. In addition, the input shaft carries a brake disk 164 at the end opposite the driven sprocket 112. The brake disk 164 cooperates with a caliper arrangement 166 to form a brake arrangement 168. The brake disk 164 is secured to the shaft 114 with a hub 170. Of course, other braking arrangements also are possible; however, the illustrated arrangement renders a compact construction that effects braking of both independently driven rear wheels 26 with a single brake disk 164.

The input shaft 114 also carries a number of gears. The forward gear 152 and the reverse gear 150 are disposed on the shaft 114 to allow the gears 150, 152 to freely rotate relative to the shaft. The transfer gear 148 is splined to the shaft 114 such that it is fixed for rotation with the shaft 114. The transfer gear 148, however, can translate along the shaft 114. The transfer gear 148, as described above, allows the operator to selectively couple in input shaft 114 with either the reverse shaft 128 or the forward shaft 126.

A transfer shaft 172 also is jounaled by bearings 174 that are positioned within the illustrated case 120. The transfer shaft 172 carries a number of gears that are used to drive an output arrangement. A forward transfer gear 176 is engaged with the forward gear 152 and a reverse transfer gear 178 is engaged with a gear positioned on the reverse shaft 128. The two transfer gears 176, 178 preferably are affixed for rotation with the shaft 172.

The shaft 172 also carries a brake gear 180. The brake gear 180 forms a portion of a transmission parking brake assembly 182. With reference to FIG. 5, the transmission parking brake assembly 182 comprises a biased lever 184 that can be brought into engagement with the gear 180 to lock the gear 180 (and the shaft 172) from rotation. The lever 184 preferably is biased with a torsion spring 186 such that the lever is not engaged with the gear 180. The other end of the lever 184 rides along a surface of the shifting shaft 134 and moves radially outward when the shifting lever is placed in a park position. Thus, movement of the shifting lever into a park position effects outward movement of the first end of the lever 184 against the biasing force of the spring 186 and the other end of the lever moves into engagement with the brake gear 180.

The intermediate shaft 172 drives an output arrangement 190 that will be described with reference to FIG. 6. The output arrangement 190 involves a constant-velocity coupling 192 that generally comprises a gear portion 194 and a housing portion 196. In the illustrated arrangement, the two portions 194, 196 are integrally formed; of course, in other arrangements, the two portions can be separately formed and affixed together to form a single output arrangement 190. Combining the two couplings 192 into a single housing member 194 allows the two couplings 192 to be arranged more compactly. More particularly, the two couplings 192 can be moved closer to the centerline of the vehicle by forming them in a single member. In addition, the drive gear portion 194 being formed integrally with both of the couplings 192 allows for a more compact transmission arrangement.

The output arrangement 190 is journaled for rotation within the casing 120, 122 by a set of bearings 200 and the casing is sealed by a set of seals 202. The housing portion is generally cylindrical and includes a shoulder that the bearings 200 seat against to secure the output arrangement in axial position.

The output arrangement 190 allows for plunging movement of one of the rear wheels 26 relative to the other. The illustrated housing portion 196 includes an inner cylindrical surface 204 having at least one cylindrical bore 207. Preferably, a series of bores that are symmetrically positioned about the surface 204 is used. In one arrangement, a set of three channels or bores is used. The bores or channels 207 at least partially carry a set of balls 206. While a part of each bore 207 is formed in the inner surface 204, the balance of the bore is formed by at least a cage member 210. In some arrangements, the bore 207 also includes a portion formed by an inner member 209 or a half shaft 208.

The half shafts 208 extend into the housing portion 196 and are connected for rotation with the housing portion 196 through a suitable connection. For instance, at the end of the illustrated half shafts 208, the inner members 209 are splined in position. The inner members 209 can be secured in position using a threaded fastener and washer, for instance. Of course, snap rings, clips and other fastening arrangements also can be used. In one arrangement, the inner members 209 are integrally formed with the half shafts 208.

The inner members 209 are received within the cages 210. As indicated above, the inner members 209 preferably also are grooved to receive the balls 206 while the outer surfaces of the inner members 209 preferably are ground to a sphere. The cage 210 preferably is ground on its inside to fit the outer surface of the inner member 209 while its outer surface is ground to a second sphere that offsets from the first sphere. Thus, the outer surface of the cage 210 preferably fits closely the cylindrical inner surface 204 of the housing portion 196. In this manner, the cage 210 can move along the bore of the housing portion 196. The offsetting spherical surfaces keeps the plane of the balls in a plane bisecting the angle between the shaft axes in order to keep the constant velocity ratio. Advantageously, the balls form a dynamic coupling between the bores and the cages (along with the other illustrated components, such as the inner members 209). Other dynamic couplings, such as the use of needle bearing or other suitable configurations also can be used.

The housing portion 196 also comprises a set of inner spaces 220 that are defined between the inside surfaces of the cages 210 and a dividing wall 222 that separates the two sides from one another. Advantageously, the dividing wall also reinforces the housing portion 196 and, thus, is preferably located in an area that lends support to the outer geared surface. In the illustrated arrangement, the wall is positioned within a plane defined by the geared surface.

The inner spaces 220 preferably are filled with grease or other lubricant. The grease lubricates the inner members 209 and the balls 206. The illustrated arrangement advantageously reduces unequal distribution of the grease from one inner space to the other. For instance, due to the dividing wall 222, the grease cannot be forced into one inner space 220 or the other under centrifugal loading or during cornering. Thus, shifting of lubricant can be eliminated.

Of course, in some arrangements, the wall 222 can be eliminated. In these arrangements, the grease is trapped between the two cages 210 and unequal lubrication is not an issue. If the inner spaces 220 are joined and the housing portion 196 is formed as a tube, then the inner diameter within the housing portion 196 preferably is substantially constant throughout. Such a configuration can further reduce the distance between the outer cylindrical surfaces of the housing portion 196. Thus, the distance between the inner members 209 can be reduced and the overall lateral dimension of the output arrangement can be reduced. This translates into a further improved range of movement for the half shafts 208.

With reference again to FIG. 3, the half shafts 208 are joined to stub shafts 230 of the wheels 26 using a further constant-velocity couplings 232. The stub shafts 230 are journaled within the carrier hub 70 in a known manner. The constant-velocity couplings can be any suitable constant-velocity coupling.

With reference now to FIG. 5, the final drive 81 preferably is arranged for pivotal movement relative to the frame assembly 22. By pivoting the final drive 81, the tension in the flexible drive element 116 can be adjusted. To this end, the casing 122 preferably includes a pivot member 250. The pivot member 250 connects to a set of brackets 252 that are attached to the frame assembly 22. Thus, the final drive 81 can be pivoted about this pivot member 250.

A second set of brackets 254 are connected to the frame assembly 22 and include a slot 256. The casing 120 includes a boss with a further pivot member 260. Together, the pivot member, the slot and the bracket define a tension adjustment region 258. The pivot member 260 can be secured in position along the slot through any suitable technique, such as a lock 259. In the illustrated arrangement, the pivot member 260 includes a threaded member 262 (i.e., a bolt) to which a nut 264 can be secured. The nut 264 and a washer can be used to friction load the pivot member 260 in position along the bracket 254. It is anticipated that the bolt can be replaced by threaded inserts, stub shafts, and the like. The bracket 254 also can include a number of settings defined by transversely extending slots such that a particular slot can be selected to alter the tension setting T.

The angular positioning of the final drive 81 relative to the frame assembly 22 also can be adjusted using the support rod 270. The support rod 270 generally comprises a tie rod 272 and a pair of turnbuckles 274. One of the turnbuckles preferably is positioned along a cross member 275 that extends between the two sides of the frame assembly 22. The other turnbuckle connects to the casing 120. By adjusting the turnbuckles 274, the tie rod 272 can be adjusted such that the relative position of the final drive 81 and the frame assembly 22 can be adjusted. The support rod eases the task of increasing the tension in the flexible transmitter because the support rod can be turned relative to the turnbuckles to separate the turnbuckles. For this reason, among others, the turnbuckles have opposing threads (i.e., turning the support rod spreads the turnbuckles rather than translates the support rod). Additionally, the support rod can include a hex portion or other surface configuration to allow a wrench or the like to grip the support rod for turning.

The split shafts 208 each rotate about a center axis E. An angle Θ is defined between the axis E and the axis C. This angle defines the angle at which the shaft 208 is extending relative to a generally horizontal plane (such as that defined by the ground or the undercarriage of the vehicle 20).

Thus, the illustrated arrangement provides a drive unit, which is easy to install during production operations. The drive unit features a final drive that is separated from the engine and that is connected to the engine by a flexible transmitter. The flexible transmitter can be easily retensioned due to a pivotal connection between the final drive and a frame of the vehicle. The final drive, however, can be rigidly fixed in position to oppose reaction forces during vehicle operation. In addition, the construction of the illustrated final drive increases the clearance zone over standard chain driven rear axles because of the placement of the larger driven sprocket in an upper portion of the final drive.

Although the present invention has been described in terms of a certain embodiment, other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. For instance, various components may be repositioned as desired. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow. 

What is claimed is:
 1. An all terrain vehicle comprising a frame, an engine compartment being defined within said frame, an engine mounted within said engine compartment, said engine being coupled to a final drive, said final drive comprising a casing, the casing defining a transmission chamber, a shaft being disposed within said transmission chamber and carrying an output gear, said output gear directly driving a constant velocity coupling, said constant velocity coupling comprising a housing, said housing comprising a geared outer surface, a first inner chamber and a second inner chamber, said geared outer surface defining a first imaginary cylinder disposed around an axis, said first inner chamber and said second inner chamber defining a second imaginary cylinder disposed around said axis, a first cage member being disposed in said first inner chamber and a second cage member being disposed in said second inner chamber, a first set of ball members securing said first inner chamber and said first cage member together for rotation and a second set of ball members securing said second inner chamber and said second cage member together for rotation, and a first half shaft extending into and connected to said first cage member and a second half shaft extending into and connected to said second cage member.
 2. The vehicle of claim 1, wherein said housing is formed as a single member.
 3. The vehicle of claim 1, wherein said housing is journaled in said casing by two sets of bearings.
 4. The vehicle of claim 3, wherein said housing has a pair of shoulders that said two seats of bearings seat against.
 5. The vehicle of claim 1, wherein each of said first inner member and said second inner member respectively connects said first half shaft to said first cage and said second half shaft to said second cage.
 6. The vehicle of claim 5, wherein said first inner member and said second inner member are secured to said first half shaft and said second half shaft respectively with mechanical fasteners.
 7. The vehicle of claim 6, wherein said mechanical fasteners comprises bolt and washer assemblies.
 8. The vehicle of claim 5, wherein said first inner member is grooved to accept said first set of ball members and said second inner member is grooved to accept said second set of ball members.
 9. The vehicle of claim 1, wherein said first cage and said second cage are adapted for axial movement in said first chamber and said second chamber respectively.
 10. The vehicle of claim 1, wherein a first inner space and a second inner space are defined within said first chamber and said second chamber between said first cage and said second cage with said first inner space and said second inner space being separated by a dividing wall.
 11. The vehicle of claim 10, wherein said dividing wall is axially aligned with said geared surface of said housing.
 12. A constant velocity coupling comprising a housing, said housing comprising a geared outer surface, a first inner chamber and a second inner chamber, said geared outer surface defining a first imaginary cylinder disposed around an axis, said first inner chamber and said second inner chamber defining a second imaginary cylinder disposed around said axis, a first cage member being disposed in said first inner chamber and a second cage member being disposed in said second inner chamber, a first half shaft extending into and connected to said first cage member and a second half shaft extending into and connected to said second cage member, a first dynamic coupling securing said first half shaft to said first inner chamber for rotation and a second dynamic coupling securing said second half shaft to said second inner chamber for rotation.
 13. The coupling of claim 12, wherein said first inner chamber and said second inner chamber are separated by a dividing wall.
 14. The coupling of claim 13, wherein said dividing wall is axially aligned with said geared outer surface.
 15. The coupling of claim 13, wherein a first space is defined between said first cage and said dividing wall and a second space is defined between said second cage and said dividing wall.
 16. The coupling of claim 15, wherein said first space and said second space are packed with grease.
 17. The coupling of claim 12, wherein said first dynamic coupling and said second dynamic coupling comprise balls that slide within grooves.
 18. The coupling of claim 17, wherein a first inner member is disposed between said first half shaft and said first cage member and a second inner member is disposed between said second half shaft and said second cage member.
 19. The coupling of claim 18, wherein said grooves are defined in said first inner member and said first chamber and said grooves are defined in said second inner member and said second chamber.
 20. The coupling of claim 12, wherein said housing is formed of a single piece. 